“They were liquidating the Free Syrian Army, one battalion at a time,” Shehabi said. “They would have continued until the whole country was under their control, if it hadn’t been for the unification of the rebels recently.”

The former prisoners tell their interviewer of how various categories of detainees were summarily executed, sometimes in front of them.

“They took a 15-year-old boy, and accused him of being a shabbih [pro-regime thug],” one man said.

“They pulled out his fingernails, and got him to finally confess to raping three women – a 15-year-old, only this tall,” the man said, gesturing to indicate the ridiculousness of the charge.

“Two Kurds were tortured and accused of being members of the PKK,” another detainee said, referring to the Kurdish party that is seen as being in league with the Syrian regime. “They never confessed ... One of them was shot right in front of us; they put a pistol to his head and shot him. The guy couldn’t even speak Arabic.”

Captives of ISIS were often forced to drink salty water, and kept for days at a time blindfolded, the detainees said. They were often forced to pray without being allowed access to water to perform ablutions beforehand, the captives alleged.

“Sometimes they made us pray with our hands tied behind our back,” one man says.

The captive rebels were often berated with the question, “What’s the difference between you and the regime?” one man alleged.

A third, much shorter video purported to show a 10-year-old who was liberated from his ISIS captors. The boy was clearly traumatized and hardly able to answer questions about his detention.

Cilina Nasser, a researcher in the Middle East and North Africa Program of Amnesty International, based in London, said the organization was very concerned about the fate of remaining detainees held by ISIS as the campaign against the extremist group intensifies.

The organization produced a report last month on the situation in ISIS detention facilities in Aleppo and the city of Raqqa, based on the testimony of former detainees.

She said the testimony of former detainees was consistent with regard to uncompromising hostility of ISIS members to the Syrian uprising.

Nasser said that the emirs, or leaders of ISIS, regularly told detainees that “we’re not here for freedom,” and that “this revolution is an infidel revolution.”

The group doesn’t have a global figure for the number of detainees of ISIS throughout Syria, and ISIS is believed to administer a number of secret detention facilities, in contrast to the Qadi Askar facility, which the public in Aleppo was well aware of.

“We’re very concerned that in other areas where ISIS is feeling the heat and losing its battles, it might lead to killings in these detention centers,” Nasser said.

Asked under what conditions individuals were being freed by their ISIS captors, Nasser said that the reasons were unclear.

“It’s similar to the treatment by the authorities, when a person is detained and then released, and they don’t really know why.”